Generally, color imaging devices, such as complementary metal oxide semiconductors (CMOSs) and charge coupled devices (CCDs), include light detectors and a color filter installed on the light detectors. The color filter is provided with filter segments of three complementary primary colors, i.e. red, green and blue colors, to separate colors.
In recent years, demand has increased for color filters mounted on imaging devices, such as CMOSs and CCDs, to achieve ideal light separation of the imaging devices without affecting the transmission regions of other colors (e.g., so that no blue transmission region exists in a green transmission region).
To meet this demand, a mixture of a blue pigment and a violet pigment is currently used. However, the pigment mixture suffers from an increase of a transmission region at 600-700 nm, which corresponds to the red region of visible light. Further, as the proportion of the violet pigment in the pigment mixture increases, the transmittance in a blue transmission region decreases.
Efforts are being made to achieve more distinct color separation, and in particular better color separation between blue and green regions, by allowing light of shorter wavelengths to transmit through the blue region and light of longer wavelengths to transmit through the green region. However, color separation characteristics of conventional pigment compositions for electronic materials are not satisfactory.
Pigments have been widely used in various applications, including paints, printing inks, color displays, and the like. In these applications, pigments are commonly dispersed in suitable media, such as organic solvents.
To attain high transmittance of the pigment dispersion compositions, the pigment particles must have a small primary particle size below a predetermined limit and must have a spherical shape. Pigment having a primary particle size above the predetermined size limit of the pigments cannot be expected to have the same transmittance after dispersion.